The scheduals go by miles, but the main thing that breaks down our brake fluid is moisture and the main variables that play into that are local humidity, water exposure, and time. Time may be number 1. My bike is still fairly low miles as I purchsed it last July and some sh.. happended soon there after that limited my riding and now its Winter. This bike is also an '02 holdover that was made just before the welding recall VINs. So its been sitting around. Do I flush out the old and install new or go by the schedule. Brake fluid is no fun to work around IMHO.